Using secondary data has many advantages, but there are also many limitations, including the lack of relevant information. This article draws on a previous study that used secondary data to investigate substance use in young, elite athletes. Three types of missing data appeared: missing data, lack of information about the data collection process, and unavailable data. Other concerns were also highlighted, such as coverage and sampling errors. The impacts of secondary data on scientific research results can be divided into unavoidable changes and researchers' choices. The research question should guide the option to use secondary data, and it is essential to assess the level of constraint that will result from it early on. Additionally, along with the quality of information available, consistency in questionnaires is vital for broadening the scope and ensuring research progress.